1. Field of the Invention
The present invention relates to an electrooptical device comprising thin film transistors formed over an insulating substrate and an IC chip formed over the same substrate, particularly to a structure of an active matrix type liquid crystal display device.
2. Description of the Related Art
In recent years, a technique for forming a thin film transistor (hereinafter referred to as a TFT) of a semiconductor thin film formed over a glass substrate has been developed. Moreover, an electrooptical device in which a voltage applied to an optical modulating layer held between a pair of substrates is controlled by a TFT to carry out an ON/OFF operation of light, has been developed.
Particularly, as a display such as a viewfinder of a video camera or a monitor screen of a note-sized personal computer, the demand for a liquid crystal panel using a liquid crystal as an optical modulating layer is rapidly increasing.
At present, the main current of development is a liquid crystal panel constituted by polysilicon TFTs using crystalline silicon films (typically polysilicon films) as semiconductor thin films. Since the operating speed of the polysilicon TFT is faster than an amorphous silicon TFT, it is possible to form a monolithic liquid crystal panel in which a pixel matrix circuit and a driving circuit (shift register and the like) are formed on the same substrate.
Further, it is desired to realize a system-on-panel in which not only a driving circuit such as a shift register but also a logic circuit such as a clock control circuit, a memory circuit, and a signal conversion circuit is formed on the same substrate.
Since such a logic circuit requires an operating speed as high as the GHz order, a polysilicon TFT is also required to have an extremely high operating speed. In order to realize such requirement, it is necessary to make a circuit element minute according to the scaling law.
However, it is very difficult to form a fine pattern with a wiring width of 1 xcexcm or less on a generally used large glass substrate. For example, in the glass substrate, there occurs a problem such as undulation and shrinkage of the surface of the substrate. Moreover, it is very difficult to realize such an optical system as is capable of forming a fine pattern in a wide range, so that the formation of a fine pattern is restricted also by the development of a light exposure technique in an aspect.
Thus, at present, it is the limit to form a driving circuit such as a shift register on the same substrate (nevertheless, the operating speed is insufficient so that divided driving is carried out), and other logic circuit is provided by an external IC.
In the present day in which a lightweight, thin, short, and small device is desired, the electrooptical device is also required to become small and lightweight to the utmost. However, even if a driving circuit is made built-in to increase the functionality of a liquid crystal panel, as long as an external IC is attached to the liquid crystal panel, it anyway becomes an obstacle to making a device miniaturized and lightweight.
The present invention has been made in view of the above problems and an object of the present invention is to provide an electrooptical device superior in portability and functionality by further systematizing a liquid crystal module.
According to an aspect of the present invention, an electrooptical device comprises a first substrate; a second substrate; and an electrooptical modulating layer disposed between the first substrate and the second substrate, wherein: a plurality of thin film transistors constituting a pixel matrix circuit, a source driving circuit, and a gate driving circuit, and at least one IC chip constituting a logic circuit are disposed on the first substrate; the first substrate and the second substrate are bonded to each other in such a manner that all edges except one edge are trued up each other between the first substrate and the second substrate; and the IC chip is attached to the first substrate adjacent to the one edge.
According to another aspect of the present invention, an electrooptical device comprises a first substrate; a second substrate; and an electrooptical modulating layer disposed between the first substrate and the second substrate; wherein: a plurality of thin film transistors constituting a pixel matrix circuit, a source driving circuit, and a gate driving circuit, and at least one IC chip constituting a logic circuit are disposed on the first substrate; the first substrate and the second substrate are bonded to each other in such a manner that all edges except a portion where an FPC (Flexible Print Circuit) is attached are trued up each other between the first substrate and the second substrate; and the IC chip is attached to the portion where the FPC is attached.
According to still another aspect of the present invention, an electrooptical device comprises a first substrate; a second substrate; and an electrooptical modulating layer disposed between the first substrate and the second substrate; wherein: a plurality of thin film transistors constituting a pixel matrix circuit, a source driving circuit, and a gate driving circuit, and at least one IC chip constituting a logic circuit are disposed on the first substrate; the first substrate is exposed only at a portion where an FPC is attached; and the IC chip is attached to the portion where the FPC is attached.
In the present invention, a liquid crystal layer is disposed between the first substrate and the second substrate to form a liquid crystal panel. At this time, although the second substrate is bonded onto the first substrate, edges (side faces) of the respective substrates are trued up each other, which is the feature of the present invention.
This structure can be obtained by cutting the first substrate and the second substrate together, or by cutting at the same position from both sides of the front and back.
However, only at the portion where the FPC is attached, the first substrate must be exposed by removing the second substrate. Thus, since the first substrate is always exposed only at that portion, that portion is effectively used as an attachment portion of IC chips.
The present invention is intended to keep the size of the first substrate to a necessary minimum by effectively using the exposed portion of the first substrate, which is conventionally used only as an attachment portion of an FPC, as an attachment portion of an IC chip.